I have a bunch of SYS-Roll dolly’s but unless I have a SYS MIDI in the stack I think they take up too much space in my crowded shop. I started making dolly’s with 3/4” plywood the same size as the SYS base and 2” hard plastic casters. Even on my lumpy concrete basement floor a seven foot stack is stable enough and with the hard plastic wheels it’s easy enough to move. A group of four requires about 2 square feet less space than four SYS-Rolls.